The present invention relates to a rotor shaft of an open-end spinning rotor having a peg-like shaft end with a reduced diameter and a front-end supporting surface which can be arranged at a step bearing, said supporting surface being provided with a wear-resistant insert.
A rotor shaft of this type is prior art in German published patent application 196 52 507. A step bearing housing filled with a lubricant is arranged at the end area of the rotor shaft, which step bearing housing is provided for the purpose of inserting the rotor shaft with a larger and a following smaller opening, whereby these openings form sealing gaps in relation to the rotor shaft during operation. The larger opening is arranged at the normal diameter of the rotor shaft, the smaller opening at the peg-like shaft end.
In the case of the high speeds for open-end spinning rotors strived for today, the dimensions of the rotor shaft play a not unimportant role, as even the smallest increase in the critical speeds of the rotor shaft can lead to higher operational speeds of the open-end spinning rotor and thus in the open-end spinning machine overall. For this reason it is no longer sufficient to give the peg-like shaft length such dimensions that only the best possible sealing of the end area of the rotor shaft is achieved in relation to the step bearing housing filled with lubricant; rathermore, the peg-like shaft end must be given dimensions to also provide an increase of the critical speed of the rotor shaft overall.
It is an object of the present invention to optimize a rotor shaft of the above mentioned type not only in regard to its sealing properties at the step bearing but also in regard to high critical speeds.
This object has been achieved in accordance with the present invention in that the reduced diameter of the peg-like shaft end measures at least 0.68 times the diameter of the rotor shaft and at least 0.82 times the length of the peg-like shaft end.
The above mentioned dimensions of the peg-like shaft end were empirically optimized according to the object of the invention and are in particular suited to a diameter of the rotor shaft which lies in the range of between 8.0 and 8.3 mm. If a diameter of the rotor shaft goes below 8.0 mm, the critical speed of the open-end spinning rotor overall would be lowered, whereas if a diameter of 8.3 mm is exceeded, the speed of the tangential belt driving the open-end spinning rotor would be so high that the lifetime of the tangential belt would be impaired. The peg-like shaft end adapted to the above diameter range is more compact than the standard shaft end used up to now, that is, even in the area of the reduced diameter, it is somewhat larger and overall shorter. Optimal dimensions were reached when the reduced diameter of the peg-like shaft end measured approximately 0.7 times the diameter of the rotor shaft and approximately 0.9 times the length of the peg-like shaft end.
The wear resistant insert, which can, for example, be designed as the support surface comprising the ceramic pin, should not be neglected in the above considerations. It has been shown that the peg-like shaft end is extended by between 0.1 and 0.5 mm by the wear resistant insert. Longer extensions have, however, a negative effect on the level of possible operational speeds of the open-end spinning rotor.